A conventional planetary gear module includes an inner gear and multiple planetary gears. A sun gear is mounted on an output end of a motor, so that the power of the motor is output via the sun gear. The sun gear is inserted in the center of the inner gear. The planetary gears are interposed between the sun gear and the inner gear. Each planetary gear is engaged at one side with the sun gear and engaged at another side with the inner gear. Therefore, the output power of the motor is adjusted by the planetary gears and then transmitted to the inner gear.
However, the conventional planetary gear module does not effectively reduce a rotational speed, and also have trouble achieving a large torque or enabling a motionless state. When the inner gear is used to lift or lower a heavy object, the planetary gears can be rotated when the sun gear is not driven by the motor. The weight of the heavy object exerts a force to rotate the inner gear, and consequently, the heavy object will be pulled down at high speed by its own weight after the heavy object arrives a desired position or during a process of conveying the heavy object to a lower position.
In view of this, the inventor studied various technologies and created an effective solution in the present disclosure.